I would make sure you have Cat6 cables run into your shop from the house. Everything else can be done later.
Also, if you already know where you want cameras if any around your garage or house, I would run network cable to those locations as well. Wireless is just not reliable enough for the amount of data that is transferred from a high resolution camera.
As far as security system. I chose to install DSC professional alarm system myself. I used a combo of wired / wireless contacts, motion sensors and smoke/ carbon monoxide detectors. I then had it monitored with Eyezon.com network alarm monitoring service. I pay about $8.95 a month and I have about $750ish in my own equipment.